1. Technical Field
Embodiments of the present disclosure relate generally to electronic filters, and more specifically to a charge pump and active filter for a feedback circuit.
2. Related Art
A feedback circuit is, generally, a circuit in which a portion of an output signal (e.g., output voltage or output current) of the circuit is combined with an input signal of the circuit. Examples of feedback circuits include phase-locked loops (PLL), delay-locked loops (DLL), etc. The portion of the output quantity that is fed back for combining with the input signal is termed a feedback signal. The feedback signal may be combined with the input signal in a suitable manner (for example, compared with, added to or subtracted from the input signal) to generate an error signal. A physical quantity proportional to the error signal may be generated by a corresponding component of the feedback circuit. The physical quantity may then be filtered and provided to a component that generates the output signal.
For example, in a PLL, the phase of an output clock (or a sub-multiple of the output clock) may be compared with a phase of an input clock. A phase-frequency detector (PFD) may receive the output clock and the input clock, and generate signals indicating whether the phase of the output clock leads or lags the phase of the input clock. A charge pump circuit receives the signals generated by the PFD, and generates positive and/or negative current pulses proportional to the pulse widths of the signals, based on whether the phase of the output clock leads or lags the phase of the input clock. A filter is typically used to perform low-pass filtering of the current pulses generated by the charge pump. The filter may be implemented using active components (components that require a power supply to operate), such as transistors, operational amplifiers, etc. The filtered signal may be provided as a control voltage to a voltage controlled oscillator (VCO), which generates the output signal, the frequency of the output signal being proportional to the control voltage.
Several embodiments of the present disclosure are directed to a charge pump and an active filter used in a feedback circuit.